Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$109.50	12.695%	$123.401	$123.40	$123.40	$123.40
Purchase #2	$82.71	4.151%	$86.1433	$86.14	$86.15	$86.10
Purchase #3	$204.97	7.226%	$219.7811	$219.78	$219.80	$219.80
Purchase #4	$86.63	13.408%	$98.2454	$98.25	$98.25	$98.20
Purchase #5	$165.76	8.386%	$179.6606	$179.66	$179.65	$179.70
Purchase #6	$97.70	13.648%	$111.0341	$111.03	$111.05	$111.00
Purchase #7	$156.65	6.372%	$166.6317	$166.63	$166.65	$166.60
7 purchase totals =	$903.92		$984.8972	$984.89	$984.95	$984.80